Cowstrtjctioit of bridges



UNITE J. B. GRIDLEY, OF BROOKLYN, NEW YORK.

CONSTRUCTION OF BRIDGES.

Specification of Letters Patent No. 9,093, dated July 6, 1852.

l To all whom it may concern:

Be it known that I, J. B. GRIDLEY, of Brooklyn, in the county of Kings and State of New York, have invented a certain new and useful Improvementin Bridges; and I do hereby declare that the following is a full, clear, and exact description of the same, reference being had to the accompanying drawing, forming part of this speciication, in which- Figure l is a longitudinal elevation with th-e outer sheathing for half of the span removed. Fig. 2, a diagram illustrating more fully my improvement; Fig. 3, an edge View of one of the tie timbers.

The same letters of reference denote corresponding parts throughout the several figures.

My invent-ion refers to the structure of wooden frame bridges, and the nature of it consists in a peculiar aplication of counterbraces acting in combination with a main brace extending from either end of the lower chord and meeting the upper chord at its center, the upper and lower chords being connected by tie timbers and the said counterbraces inclining in opposite directions above and below the main brace which they connectwith the upper and lower chords, whereby, when weight is applied to the bridge, the tendency of the upper and lower chords is to sink in the middle and the extremit-ies to approach the center and the feet of the main brace to move in an opposite direction, said movement being resisted by the actions of the counterbraces which divert the strain and apply athrust upward and in direction either way of the length of the bridge.

To enable others skilled in the art to make and use my invention I will proceed fully to describe it.

In Fig. l which exhibits an exterior elevation of one side of the bridge, or it may represent one of a series of upper and lower chords-dependent in number upon the re quired breadth of the. bridge, A is a top and B a bottom chord, of any desired breadth or thickness, and extending from pier to pier C. I) are tie-timbers uniting the top and bottom chords. They may be of any requisite number and arranged in pairs transversely at any suitable distances apart from one another as seen in Fig. 3, having openings or spaces between them for the entrance of or passage through of the counter and main braces, the center tie-timber forming the king post. E are diagonal main braces. They are firmly secured, at their lower ends by stirrups to the lower chordon its top surface and meet at the center of the top chord, on its under surface, where they are united by any appropriately constructed metal step a. F are upper and Gr lower counterbraces. They connect the main brace and upper and lower chords through suitable metal chairs 2),' the said upper and lower counter-braces incline in reverse direction to one another as follows the lower counterbraces G, for either half of the span, incline upward away from the nearest pier, while the upper ones F incline reversely though at varied angles thereto, the top ones F increasing each succeeding one to approach the horizontal position and being shorter as they approximate the center of the bridge, while the lower ones G similarly vary in the opposite direction, the upper counter braces connecting the main brace with the upper chord while the lower counterbraces unite the main brace with the lower chord.

By this combination of chords, tie-timbers, main braces and counterbracesconstructed and arranged as described, it is obvious that a weight or strain brought upon the bridge at its center will have a tendency to depress the chords at the middle bringing the outer ends toward each other, so that the counterbraces F, Gr, in having the strain communicated to them, will, by their inclined positions, press so as to exert a tendency to expand the upper and lower chords in direction of their length from the center and to counteract the expansion of the main brace, the upper 'counterbraces F also serving, by the deflection. of the top chord, and straightening of the main brace, to press upward against the top chord, while the lower counterbraces Gr, in pressing downward combine to throw a direct tension upon the tie timbers, which result, together with the specified effect of the counter-braces to divert the strain longitudinally of the chords and main brace, applies the sustaining weight in direction of the fiber. These results will be clearly seen by reference to the diagram in Fig. 2, wherein A represents the top chord, B the lower one D the tie timbers, E the main brace, F the upper and G the lower counter braces, W a weight applied to the crown in illustration of the strain which from the top cho-rd will be thrown directly upon the main brace, from thence transmitted through the counter braces to the top and bottom chords and tie-timbers in the manner specified.

Instead of the double diagonal main brace E, an arch (its equivalent) may be employed.

I am aware that diagonal or inclined counterbraces differently arranged have before been used, such therefore, irrespectiveof their disposition and combination as specified I do not claim. But

nesses.

J. B. GRIDLEY. Witnesses:

ALFD. GREGORY,

A. E. H. JOHNSON. 

